Field of the Invention
The invention relates to a circuit configuration for controlling the transmitting power of a battery-operated transceiver having a battery for providing a supply voltage and a power stage for the controllable amplification of a radio-frequency signal.
Mobile transceivers, especially cellular digital mobile telephones, are supplied with voltage by a battery. The higher the transmitting power of the mobile telephone, the higher the current drawn from the battery. The current flowing through the battery produces a voltage drop across its internal impedance. When the current is higher, the voltage provided for the circuit to be supplied correspondingly drops. That loaded voltage is therefore lower than an idling voltage. If the operating voltage supplied by the battery is no longer sufficient for proper operation of the mobile transceiver, the device is switched off.
In mobile telephones, a power output stage generating the transmitted signal used for radiation can be connected directly, i.e. without buffering, together with other circuit units of the mobile telephone, to the battery. The other loads can be digital circuits such as microcontrollers, digital signal processors, reference clock generators, etc. Due to digital system control, switching-off as a result of inadequate supply voltage is determined by those last-mentioned loads. Current consumed additionally due to the higher transmitting power, and an additional voltage drop generated as a result across the internal impedance of the battery, causes the device to be switched off earlier. A nominal power of the mobile telephone is individually calibrated during production.
It is a problem that the battery is rapidly discharged, especially with a high transmitting power, and a telephone call can be abruptly terminated by the automatic switching-off control without the operator being able to react with sufficient speed. That restricts the ease of operation and the possible uses of such mobile telephones.